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From: Waiman Long <longman@redhat.com>
To: "Paul E. McKenney" <paulmck@linux.ibm.com>,
	Josh Triplett <josh@joshtriplett.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	Joel Fernandes <joel@joelfernandes.org>
Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
	Waiman Long <longman@redhat.com>
Subject: [PATCH] rcu: Force inlining of rcu_read_lock()
Date: Tue, 21 May 2019 16:48:43 -0400	[thread overview]
Message-ID: <20190521204843.11060-1-longman@redhat.com> (raw)

It is found that when debugging options are turned on, the
rcu_read_lock() function may not be inlined at all. That will make
it harder to debug RCU related problem as the print_lock() function
in lockdep will print "rcu_read_lock()" instead of the caller of
rcu_read_lock() function. For example,

[   10.579995] =============================
[   10.584033] WARNING: suspicious RCU usage
[   10.588074] 4.18.0.memcg_v2+ #1 Not tainted
[   10.593162] -----------------------------
[   10.597203] include/linux/rcupdate.h:281 Illegal context switch in
RCU read-side critical section!
[   10.606220]
[   10.606220] other info that might help us debug this:
[   10.606220]
[   10.614280]
[   10.614280] rcu_scheduler_active = 2, debug_locks = 1
[   10.620853] 3 locks held by systemd/1:
[   10.624632]  #0: (____ptrval____) (&type->i_mutex_dir_key#5){.+.+}, at: lookup_slow+0x42/0x70
[   10.633232]  #1: (____ptrval____) (rcu_read_lock){....}, at: rcu_read_lock+0x0/0x70
[   10.640954]  #2: (____ptrval____) (rcu_read_lock){....}, at: rcu_read_lock+0x0/0x70

To make sure that the proper caller of rcu_read_lock() is shown, we
have to force the inlining of the rcu_read_lock() function.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 include/linux/rcupdate.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 922bb6848813..44f80aced02b 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -588,7 +588,7 @@ static inline void rcu_preempt_sleep_check(void) { }
  * read-side critical sections may be preempted and they may also block, but
  * only when acquiring spinlocks that are subject to priority inheritance.
  */
-static inline void rcu_read_lock(void)
+static __always_inline void rcu_read_lock(void)
 {
 	__rcu_read_lock();
 	__acquire(RCU);
-- 
2.18.1


             reply	other threads:[~2019-05-21 20:49 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-21 20:48 Waiman Long [this message]
2019-05-22 18:18 ` Paul E. McKenney
2019-05-22 18:41   ` Waiman Long

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